Broaching tool for forming tapered openings in tubes



Nov. 13, 1956 BROACHING TOOL E. B. HAMMILL FOR FORMING TAPERED OPENINGS IN TUBES Filed Nov. 9, 1953 INVENTOR EDWARD B. HAMMILL A ATTORNEY BROACHING TOOL FOR FORMING TAPERED OPENINGS IN TUBES Edward B. Hammill, Winston-Salem, N. c, assignor to ,Western Electric Company, Incorporated, New York,

Y., a corporation of New York Application November 9, 1953, Serial No. 390,77 8 3 Claims. (Cl. 90-33) This invention relates to broaching fixtures and more particularly to a broaching fixture for forming tapered openings in tubes.

In high-frequency electrical apparatus such as radar equipment it would be both inefficient and impractical to conduct electrical energy in parts of the apparatus by the standard type conductors such as wires in a manner which is done at the lower frequencies. At the lower frequencies an electrical current passing through a conductor flows over the complete cross-sectional area of the conductor. However, as the frequency increases the current tends to flow only near the periphery of the conductor. This phenomenon is known in the electrical arts as skin effect, and at the extremely high frequencies at which radar equipment operates it has been long known to conduct electrical energy through tubes known as wave guide. Simply, wave guide is merely a conductor with the center portion removed since due to skin effect there is no need for this portion.

Generally, wave guide tubing is of rectangular crosssectional area and is provided in convenient lengths. To connect one length of wave guide to another or to a piece of equipment, a flange is provided at each end of a length of tubing with a plurality of holes drilled in the flange through which bolts may be passed to secure the various parts together.

These flanges are usually soldered to the end of the wave guide tubing and very often the heat from the soldering operation will tend to decrease the cross-sectional area of the wave guide or warp the wall in some manner.- If two lengths of wave guide are connected together at their flanged ends and the internal cross-sectional areas of both are not exactly the same, then a mismatch ofirnpedances will occur. To improve the impedance match of the wave guide, therefore, this mechanical mismatch caused by different internal cross-sectional areas of the joined wave guide tubing must be eliminated.

Accordingly, one object of this invention is to provide a broaching fixture with which the internal surfaces of tubing may be broached to provide a given uniform cross section.

Another object is to provide a broaching fixture with which a tapered opening may be formed internally of the tube near the end.

With these and other objects in view, the invention comprises a pair of tapered broaching cutters which are secured to a ram of an arbor press or any other suitable operating means. Positioned between the cutters is a tapered guide block which is fixed against movement by being secured to a bolster plate of the press through an interconnecting guide plate. The tubing to be broached is positioned over the tapered cutters with the smaller portions of the cutters positioned opposite the guide block. A flange on the end of the tubing is then secured to the bolster plate of the arbor press. The ram is actuated away from the wave guide flange Patented Nov. 13, 1956 'along the line 22 of Fig. 1 and indicates by dashed lines the position of the tube to be cut prior to the cutting operation;

Fig. 3 shows the elevational view of Fig. 2 with the tubing in position but with one wall cut away during the cutting operation; and

Fig. 4 is a sectional view taken along line 4-4 of Fig. 2.

Referring now to the drawings, wherein like reference numerals indicate the same elements throughout the several views, 10 designates the ram of an arbor press or any suitable power ram which is capable of reciprocable motion to the left and right as viewed in Figs. 1 to 3. Connected by suitable means to the press so that it is secured against movement is a guide plate 11. The guide plate 11 may be mounted on the bolster plate (not shown) of the press, the important feature being that it be fixedly secured against movement. A guide block 12 is secured to the plate 11 by a screw 14 and the block 12 and plate 11 are kept in their proper position by placing dowel pins in holes 16 and 17 which are defined when the block 12 and plate 11 are in correct alignment. Obviously, the plate 11 and block 12 may be an integral member or may be secured by any suitable manner other than screw 14.

The guide block 12 has opposed tapered surfaces 18 and 19 which are in straight lines respectively with tapered surfaces 20 and 21 of the plate 11, which surfaces 20 and 21, respectively, bound openings 22 and 24 of the plate 11 on one side.

Reference numerals 26 and 27 designate a pair of broaching cutters which are tapered as shown in Figs. 2 and 3, each cutter from right to left as seen in these figures being progressively thicker in cross section. The cutters 26 and 27 are secured to the ram 10 by a linkage assembly designated generally by the numeral 28. The linkage assembly 28 comprises a rod 29 which is inserted through holes 30 and 31 of the cutters 26 and 27, respectively, and hole 32 of ram 10, all of which holes have a working fit with the rod 29.

Secured at either end of the rod 29 by screws 34 and 36 respectively are washers 37 and 38. Disposed between the washer 37 and the cutter 26 is a spring 39 which tends to force the cutter 26 against ram 10. Similarly disposed between the washer 38 and the cutter 27 is another spring 40 which tends to force the cutter 27 against the ram 10.

Fig. 2 shows the position of the various elements of the broaching fixture prior to the broaching operation on a length of Wave guide tubing 41 which is rectangular in cross section and which has a flange 42 soldered at its end. The flange 42 has a plurality of holes drilled therein so that one hole lies adjacent each of the holes 4649 (Fig. 4) of the guide plate 11.

With the ram 10 at its maximum in position, that is when the ram 10 is moved to the left to its extreme position as shown in Fig. 2, the smaller portions of the tapered cutters 26 and 27 are positioned opposite the openings 22 and 24 of the guide plate 11. In this position the combined thicknesses of the cutters 26 and 27 and the guide block 12 immediately adjacent the left side of plate 11 (Figs. 13)' areless than the internal dimension of the V twoof the internal surfaces of the tubing 41, each suc-' ceeding tooth cutsaprog-ressively larger portion from the tubing and when the cutters 26 and 27 leave the tubing4 1, a taper equal to-the taper of the guide block 12 will have' been cut into-two of.the-surfaces of the tubing 41: and therequireddimension-can obviously be easily predetermined. a

. It willbe noted that as the l'amlfl moves to the'right as shown in Fig; 3, the cutters 26and'27 will move out toward the ends of the rod 29 and will tend to compress the springs 39 and 40, respectively. The force exerted by these springs 39 and.4t against the cutters 26 and 27 is such thatthe sides of the cutters Hand 27 opposite the teeth will always be flush with the tapered surfaces 18 and 19, respectively, and will not-tend to pivot about the surfaces 20 and 21-. in the guide plate 11.

When the two internal surfaces of the tubing have been tapered. as explained above, the remaining two surfaces may be tapered in a similar manner, thereby completing thedirnensioning of oneend of a length of tubing. With ends of. other lengths of tubing taperedin like manner,

these ends may be joined together by'bolting the flanges together with complete assurance that no mismatch of impedance will occur. In thexevent that the tube 41 is rectangular, 'difiercnt' width broachesmay be used for the two operations.

It is to be understood that the above described embodiment is merely illustrative of the invention and that many modifications maybe devised by those skilled in the artto which the invention pertains, and the exclusive use of all-such modifications as come within the scope of the appended claims is contemplated.

What is claimed is: 1. A fixture for cutting a plurality of tapered surfaces on the internal surface of a tube, which comprises a.

stationary plate, a block secured fixedly to the plate and having a plurality of surfaces tapered with respect to an 2. A breaching fixture for cutting a plurality of tapered surfaces on the internal surface ofa tube, which corn-v prises a stationary plate, a block secured fixedly to the plate and having a plurality of surfaces tapered with respect to an axis thereof, a plurality of tapered broaching cutters for cutting a similar number of surfaces in the tube, each of the cutters being reciprocable over a correaxis thereof, a plurality of broaching cutters each of which reciprocates over a corresponding one of the tapered surfaces, means for mounting a tube on the plate so that the cutters may be placed Within the tube prior to the broaching thereof, and means for reciprocating the cutters;

spending one'of'thetapered surfacesof: the bloek, me ans for mounting a tube on one side, ofz the' plate so'that the tube may surround the cutters prior to the broaching thereof, a plurality of openings formcd in the plate, each of the cutters passing through a corresponding onqof the openings in the plate, andnieanyforreciprocating the cutters connected to the cutters-omaisideof theglate opposite to the side on which the tube is mounted.

3. A breaching fixture for cutting-tapered surfaces in opposite internal surfaces of a rectangular tube, which comprises a stationary plate having a pair of openings therein, a block secured fixedly to the plateand liaving a pair of surfaces taperedwit-h respect to anaxis thereof; J a pair of tapered broaching cutters each" of which has a hole formed near its thinner end; is reciprocablei over a corresponding one of the tapered surfaces on the block: and abuts thereagainst,'n1eans forpositioningsuch.atubeon one side of theplate so that the cutters may be placed: within the tube prior to the breaching thereof Witheach cutter passing through a corresponding one of the openings in the plate, a reciprocable member having a hole therein formed transversely. of its axis-of reciprocation, means for connecting. the reciprocablemember to. the cut I ters so that reciprocating motion canbe imparted to the.

cutters, thejcon'necting meansincluding a rod positioned. so as to pass through the holes in-the cuttersand the hole in the reeiprocablef. member" with. thememberi disposed between the cutters, washers securedtothejends of.-the'; rod,; and a --helical-- spring; positionedraroundthe; rod and? between each washer and cuttenf'or retaining the, cutter and the tapered surfaces of the block v in-"abutting relationship.

- R cferences Cited in-thegifile ofr'this patent- UNITED sures-PATENTS 1430,133

Rice .June 6,1951) 7 

